Objective Questions on Electrical Transmission | 10

  1. Which conductors connects the consumer’s terminals to distribution?

    Correct Answer: Service Mains. There are different segments in power system transmission and distribution. After the power is transmitted from the generating station, zonal main substation distributes them into different substations through the feeder cable. There are no tapping from the feeder cable. After that the power is distributed among the service mains through the distributor cables. The tappings are taken out from the distributor cables. From the service mains, cable are locally connected with consumers terminals.

  2. The underground system cannot be operated above which voltage level?

    Correct Answer: 66 KV, actually underground cable system is most suitable for those areas, where the neat and clean distribution is required. Mainly this type of wiring is ssen in metro cities. The spaces in between the conductors are quite lesser as compared to overhead cables. So, strong insulation is provided with each cables. And after that, different layer of insulations are provided surronding those cables. Considering all those things, 66 KV is considered as the highest voltage level for underground cable system.

  3. Overhead lines can be designed for operation upto:

    Correct Answer: 400 KV, in case of overhead transmission lines, the space in between the conductors are more as compared to underground system. And additionally, air acts like the insulation medium for those cables. As those conductors are clipped at very high position, so the clearance from the ground is also ok for those cables. These all features permits togetherly for transmission of Extra High Voltage through the overhead cables. So, the huge amount of 400 KV is transmitted via the overhead lines, with suitable cables and pole structures.

  4. Which of the following material is not used for transmission and distribution of electric power?

    Correct Answer: All of those. Material with high conductivity is used in power system transmission and distribution. Most economical cables are built up with that material, which is best conductor of electricity as well as cheap too. Because the span of transmission lines is quite large, sometime overseas. So, the conductor must be cheap to ensure the economy. And for better conductivity, copper is used. Although all of those metals are used as conductor for transmission system, but alumium is prefered becuase this metal have some unique features. It is quite cheap, and the conductivity is very good, and the aluminium wires are mechanically strong.

  5. The usual span with RCC poles are:

    Correct Answer: 80 mt to 100 mt. The full form of RCC pole is Reinforced Cement Concrete. This type of poles are most suitable for low voltage transmission, like consumer areas.

  6. Galvanised steel is generally used as:

    Correct Answer: All of the above. Galvanised steel is very popular term. Conductor is one of the most vulnarable element for electrical wiring system. If the wires are made up with ordinary steels, rust or corrosion will attack the wire after some time. For this reason, galvanised wires are used in many applications. A layer of Zinc Oxide is provided on the steel wire by some chemical process. This layer protects the cables from any natural effects. Galvanised wires are used as earthing cables, wiring stray cables and also in structural elements.

  7. The corona is affected by which of the following?

    Correct Answer: All of the above. Corona is an phenomenon of transmission lines. The outer portion of transmission lines starts glowing with light violet glow, and a hissing sound is there. The air surrounding the conductors get ionised, and after that this particular phenomenon is observed. If the outer surface of the conductor is rough and irregular, then there is more chances of corona. And this phenomenon is depended upon the size, shape and surface of conductor. This is the reason for which the conductors are choosen as round shaped and smooth.

  8. High voltage transmission line use:

    Correct Answer: Suspension Insulator. Pin type insulator is suitable for medium voltage range, because the insulation is so desinged that it wound be able to handle the medium voltage. There are several parameters like puncture strength etcare associated with line insulators. In case of suspension type insulators, a series of insulator discs are arranged and according to the voltage level, the discs are designed. In fact, addition of discs are also possible for this type of insulators. Therefore, in high voltage transmission, suspension insulators are preferred.

  9. By which of the following system electric power can be transmitted?

    Correct Answer: Both overhead and underground. For high voltage transmission overhead system is preferred, because it is quite safer and lot of spaces are there in between two parallel conductors. Underground system is preferredfor those areas, where the neat and clean transmission system is required, like different metro cities.

  10. Distribution lines in India generally use:

    Correct Answer: RCC Poles. RCC means reinforced cement concrete. This type of poles are very cheap, and also very easy to construct. Concerete structure is very rigid and no effect of moisture. The distribution poles are provided in many street junctions, roads etc. As per the climate conditions and considering the economy, RCC poles are best suitable option for distribution poles in India.

  11. The square root of the ratio of line impedance and shunt admittance is called:

    Correct Answer: Surge Impedance of the line.

  12. The phenomenon of rise in voltage at the receiving end of open circuited or lightly loaded line is called:

    Correct Answer: Ferranti Effect. This phenomenon is seen in long transmission lines. If a large is opened from the line, or if the line is connected with very light load, then the receiving end voltage will be greater then the sending end voltage.

  13. A booster is a:

    Correct Answer: Series wound generator.

  14. Transmission line insulators are generally made up of

    Correct Answer: Porcelein. The transmission lines are quite long and the insulators required is very high for long transmission lines. So, the insulator must be cheap and easily available. Porecelein shows very good insulation property, even in very high voltage level. A serise of porcelein discs, or sometime pin type porcelein insulator is used in transmission lines. Glass is also very good insulator, but handling and other costs are more, therefore porcelein insulators are most widely used.

  15. The distributors for residential areas are:

    Correct Answer: Three phase Four Wire. In domestic areas, the required voltage level is 220 Volt to 230 Volt single phase. A neutral wire also needed to complete the circuit. Line voltages are suitable for industrial applications, but in domestic areas, three phase star connection is most suitable. This connection gives three different phase cables along with a common neutral wire. Each phase carries 230 Volt each, so the phases are distributed among the service mains with the neutral wire. The neutral wire is grounded at the substation via an earthing transformer.